1. Technical Field
The present invention relates generally to miniature hearing aid batteries which are volumetrically energy efficient and asymmetrically shaped for fitting deeply and comfortably in the ear canal.
2. Description of the Prior Art
(1) Conventional Hearing Aid Batteries
Hearing aids primarily rely on button cells which are symmetrically round as shown in FIGS. 1 and 2. These cells are circular in cross section with diameter (D) and height (H). The cells are generally button-shaped with diameter (D) greater than height (H) thus referred to as xe2x80x9cbutton cells.xe2x80x9d These prior art cells are constructed of a cathode (positive) can 3 crimped over an anode (negative) can 2 at crimp area 8 near the top. A sealing grommet 7 is present between the two cans. Zinc air cells, which rely on air (oxygen) in the environment as a source for their internal electrochemical reaction, are widely used in hearing aid applications due to their exceptional volumetric energy efficiency. Air hole 5 on the bottom of the cell allows oxygen from the environment to enter the cell into the cathode assembly 6 and subsequently into the anodic material 4 (zinc) inside the anode can.
(2) Brief Description of the Ear Canal and Canal Hearing Aids
The human external ear 10 is comprised of the pinna 12 and the ear canal 11, which is narrow and tortuously elongated as shown in FIG. 3. The ear canal 11 begins laterally with the canal aperture 13 and terminates medially with the eardrum 16. First and second bends, 14 and 15 respectively, are generally present and must be considered when designing a deeply inserted canal hearing device. The ear canal generally has an oval cross section (FIG. 4) with a long diameter (CDL) and short diameter (CDS).
Recent advances in miniaturization of electronics, transducers and batteries have led to the development of canal hearing aids which are partially or deeply inserted in the ear canal. Canal hearing devices are generally inconspicuous, thus very desirable for the hearing impaired who may be concerned with the social stigma and vanity associated with wearing a visible hearing aid. However, due to the complex shape of the ear canal, being elongated, contoured and oval at the cross section, the conventional cylindrical button cells used in standard canal hearing devices are inefficient in terms of volumetric utilization of the ear canal cavity. For this reason among others, canal hearing aids are notorious for requiring frequent battery replacement and being uncomfortable, particularly for small ear canals.
(3) Review of State-of-the-Art in Hearing Aid Related Battery Technology
Cretzmeyer, et al. (U.S. Pat. No. 4,189,526), Smilanich (U.S. Pat. No. 4,404,266) and Oltman et al. (U.S. Pat. No. 5,582,930) describe zinc-air button cell batteries with various improved features. These button cell batteries are made of a cathode can crimped over an anode can with a sealing element therebetween (i.e., 2 in FIG. 2 of the ""930 patent). Although each metal can may be made relatively thin, in the range of 0.114 to 0.15 mm according to the ""930 patent, the presence of two parallel walls on the circumference of the cell (2 and 3 in FIG. 1), in addition to a seal (7 in FIG. 1) therebetween, presents atriple-wall effect which adversely affects the volumetric efficiency (battery longevity/volume) for the battery assembly. This results in shorter battery life and frequent battery replacement. A battery compartment for the button cell with electrical contacts also consumes space further reducing the volumetric efficiency of the hearing device. Another source of volumetric inefficiency in conventional hearing aids is the acrylic outer shell (not shown) which represents a secondary enclosure with respect to the battery assembly within, thus consuming additional space and reducing the volumetric efficiency of the canal hearing device.
Aceti et al. in U.S. Pat. No. 6,058,198 describes a hearing aid assembly with a battery integral therewith. According to the ""198 patent, the anodic material and air-cathode assembly are contained within a unitary plastic housing along with electronic circuit and transducers (speaker and microphone). This approach eliminates the concept of a battery subassembly, thus appearing more efficient in its volumetric energy efficiency. However, combining anodic elements along with hearing aid components is not practical due to the corrosive effects of battery chemicals on electrical circuits, wires and other components within the hearing aid. Furthermore, eliminating a battery subassembly complicates the manufacturing process since the battery function cannot be independently tested or verified prior to its incorporation into the hearing device.
Leedom in U.S. Pat. No. 5,825,896 describes a hearing aid having two hinged boot portions, one of which incorporates a battery and a speaker. The ""896 patent describes the shape of the boot portion as having an elliptical cross-section which is advantageous for fitting deeply and more comfortably in the ear canal. However the ""896 patent does not specifically teach an elliptical battery assembly but rather elliptical boot portions. Furthermore, the ""896 patent does not describe the casing configuration of the battery assembly, nor does it describe the relationship between individual elements of the battery assembly, particularly pertaining to energy capacity.
In the aforementioned related ""717 application, Shennib et al. describe a battery assembly having an oval cross section when combined with a section of a hearing aid connected thereto. The battery assembly in the ""717 application is elongated and oval in cross section thus suited for fitting deeply and comfortably within the ear canal. Similarly, the ""717 application does not describe the specific relationship of the elements within the battery assembly, particularly those pertaining to energy capacity improvements. Both ""896 patent and ""717 application fail to teach the specific features and manufacturing processes which lead to improved volumetric energy capacity.
A key goal of the present invention is to provide a battery assembly with improved energy capacity and fit in the human ear canal, particularly in the bony region thereof.
Another goal of the present invention is to provide a disposable hearing aid, incorporating the invented battery assembly, and specifically suited for extended wear applications in which a hearing aid is worn continuously in the ear canal for a relatively long period of time, preferably several months.
The invention provides a volumetrically energy efficient battery assembly for use with canal hearing devices that fit deeply in the ear canal. The invented battery comprises a cylindrically elongated metal shell, a metal cup covering an opening at the base of the elongated metal shell, and a sealing element positioned therebetween for sealing the contents of the battery assembly within. The battery assembly is medially tapered with length (L) across the longitudinal axis of the ear canal when placed therein. The cross section is oval with long and short diameters, (DL) and (DS), respectively. The short diameter DS is less than the length (L) thus the battery is configured elongated and narrow to fit optimally and deeply in ear canals, which are also narrow, tortuous and oval in cross section. In the preferred embodiments, the metal shell of the invented battery assembly is structurally self-supporting and is essentially in direct exposure to the environment of the ear canal, thus eliminating the need for a secondary plastic enclosure typically used in conventional hearing aids with button cells.
In the preferred embodiments of the invention, the battery assembly is bullet shaped with oval cross section for maximum volumetric energy efficiency and optimal comfort during wear and insertion thereof in the ear canal. A hearing device employing the invented battery assembly can be made smaller because it is volumetrically more energy efficient. It is particularly suitable for extended wear applications deep in the ear canal. In the preferred embodiments of the invention, the battery assembly is manufactured and tested as a subassembly, which is then integrated into a disposable hearing aid. The hearing aid is discarded when the electrical energy of the incorporated battery assembly is depleted.